The present invention relates to a photographic film cassette, and more particularly, to a film cassette providing reliable prevention of light from reaching photographic film contained therein.
A photographic film cassette contains photographic film, e.g. negative film, in light-tight fashion in a cassette shell. The negative film is fed outside the cassette through a film passage mouth formed on the cassette shell. Light trapping fabric, or "plush", is attached to the sides of the film passage mouth by means of an adhesive agent or double-coated adhesive tape so as to contact both surfaces of the negative film. The light trapping fabric consists of black-dyed velvet made of base fabric and pile threads densely planted thereon. Making the pile threads dense fills the film passage mouth to shield the inside of the cassette shell from light.
It is known to form a cassette shell out of a plurality of molded plastic shell components. In a film cassette disclosed in Japanese Patent Laid-Open Publication No. 57-190948, the cassette shell is formed by mounting a cassette cap on a container component of thermoplastic material by inserting the cap in a direction parallel to the spool. This cassette cap covers one lateral edge of the film passage mouth, so that it is possible to shield the inside from light which comes up to the edge of the film passage mouth.
In U.S. Pat. Nos. 4,832,275 and 4,834,306, a cassette is provided with separation claws for separating a film leader from the film roll to direct it to the film passage mouth. Either annular ridges formed inside the cassette shell, or circumferential lips formed on flanges of the spool, prevent the film from becoming loose on the roll. In both patents, rotation of the spool can cause the film leader to advance through the film passage mouth. Before and after using the film in a camera, the entire length of the film is wound up and contained in the cassette shell up to its leading end.
The cassette shell of such a self-advancing film cassette consists of two molded shell halves which are separated at a juncture dividing the film passageway and including the rotary axis of the spool. The edges of the shell halves forming the juncture are provided with stepped portions which prevent light from entering the cassette shell through the juncture. Accordingly, this self-advancing film cassette is advantageous not only because of the portability of the cassette, but also because of the cassette's improved light-shielding property.
However, the construction of this self-advancing film cassette makes it difficult to retain a strong adhesion by an adhesive agent or a double-coated adhesive tape, because direct pressure to the surface of the light trapping fabric bends down the pile threads and thus decreases the light-trapping property. Attachment by means of double-coated adhesive tape is disadvantageous because it might drop down from the film passageway under a condition of high temperature and high humidity. Although, in a self-advancing film cassette as disclosed in U.S. Pat. No. 4,834,306, the force applied to the spool for advancing the film is made minimal by directing the film leader to the light trapping fabric in a middle position equidistant from both upper and lower inside surfaces of the film passageway, the film leader may not be advanced to the outside when the force for rotating the spool is insufficient to advance the film leader against the inner edges of the light trapping fabric. There is another problem in that forcing the leading end of the negative film to advance may peel off the light trapping fabric if the light trapping fabric is not attached firmly to the film passageway.
It is difficult to construct a self-advancing film cassette by means of a container component and a cassette cap, as disclosed in Japanese Patent Laid-Open Publication No. 57-190948, by adding annular ridges or separation claws as disclosed in U.S. Pat. Nos. 4,832,275 and 4,834,306, because the container component is molded integrally from plastic, though light can be shielded advantageously at the lateral ends of the film passage mouth. Thus, this construction is disadvantageous in its lack of portability and its low-shielding property in the position at the center of the film. Referring to FIGS. 14 and 15, 135-type negative film 4 recently has been provided with DX code 60, which is recorded optically on lateral edge portions 4a outside perforations 45, and which represents various information such as the type negative film 4. The code 60 also is used for printing after development.
In a cassette 113 such as that disclosed in U.S. Pat. Nos. 4,832,275 and 4,834,306, a spacing 78 is defined between upper and lower shell halves 114 and 116 inside a juncture 117 at both lateral ends of a film passage mouth 12 when edges of both shell halves 114 and 116 forming the juncture 117 are fitted together on the outside of the cassette 113. Because the spacing 78 extends inside the cassette 113, light 79 incident upon the spacing 78 enters the inside of the cassette 113 through the extension of the spacing 78. With the cassette 113 unloaded from a camera (not shown) after winding up the negative film 4 in the cassette shell, the light 79 might cause fogging on lateral edge portions 4b of the film, making the DX code illegible at the time of printing. A spacing 124 is defined between flanges 54 and the negative film 4 would on a spool 5. The light 79 through the spacing 124 also might cause fogging on the lateral edge portions 4b of a plurality of outer turns of the wound film 4.